A large earthquake has rocked Ecuador, the second of the day in an area devastated by a massive tremor one month ago.

The US Geological Survey said the latest 6.8-magnitude quake was centred below land about 15 miles north of the city of Rosa Zarate.

There were no immediate reports on the extent of damage or casualties.

Earlier, a 6.7-magnitude earthquake was recorded as being centred 21 miles from the same town.

The much larger magnitude 7.8 earthquake on April 16 killed 660 people and left tens of thousands homeless.

President Rafael Correa has increased taxes to fund the recovery from that quake, but says it will take years to rebuild the beach towns and tourist hubs left devastated.

Some previously-ravaged homes and buildings suffered more damage in the first quake on Wednesday, but there were no reports of injuries or deaths. Authorities are working to restore power in affected areas.

Jorge Zambrano, mayor of Manta, one of the areas hit hardest by last month's quake, said: ''It was a big shake and all of us were scared but there are no major problems at the moment.''